As described above, isothiazole compounds are widely known as intermediates for pharmaceuticals and intermediates for agricultural chemicals, and intermediates for functional pigments, electronic materials, etc. Therefore, as disclosed in Non-Patent Documents 1 and 2, various studies have heretofore been made on processes for producing isothiazole compounds.
Among isothiazole compounds, 3,4-dichloro-5-cyanoisothiazole, which can easily be subjected to the conversion of a functional group thereof, is known as an intermediate for pharmaceuticals and an intermediate for agricultural chemicals. In addition, as disclosed in Patent Documents 4 and 5, this compound is in fact used as an important intermediate for agricultural chemicals.
However, it has been difficult for the production processes disclosed in Non-Patent Documents 1 and 2 to produce 3,4-dichloro-5-cyanoisothiazole, which is useful as an important intermediate for agricultural chemicals.
That is, a process using carbon disulfide (CS2), sodium cyanide (NaCN) and chlorine (Cl2) has heretofore been known as a process for producing 3,4-dichloro-5-cyanoisothiazole (see Patent Document 1). However, this process has a drawback that carbon disulfide, which is a special inflammable material, is used as a raw material to be used therein. Moreover, this process also has a drawback that sodium cyanide, which is a toxic material, is used therein. Furthermore, in this process, chlorine is introduced into a reactor containing therein N,N-dimethylformamide (DMF) as a solvent with heating. However, it is well known to a person skilled in the art that when N,N-dimethylformamide and chlorine are used simultaneously, there is a possibility of the runaway of the reaction or an explosion. For these reasons, it is considered that the implementation of this process requires most careful attention and adequate measures in order to maintain safety. In addition, there is a possibility that this process cannot ensure the safety of a production plant because there is a possibility that the runaway of the reaction and an explosion occur in some cases as described above. That is, this process using N,N-dimethylformamide and chlorine at the same time is not preferred for industrial manufacture because there is concern for lack of safety.
As another process for producing 3,4-dichloro-5-cyanoisothiazole, a process using trichloroacetonitrile and sulfur is known (see Patent Document 2). However, this process has the drawback of requiring the reaction at a high temperature of 200° C. to 300° C. as described in Examples therein. In addition, this process has the drawback of requiring the use of a special raw material such as trichloroacetonitrile.
Furthermore, a process using dichlorofumaronitrile and sulfur is known (see Patent Document 3). However, this process also has the drawback of requiring the reaction at a high temperature of 230° C. to 300° C. in Examples therein. In addition, this process also has the drawback of requiring the use of a special raw material such as dichlorofumaronitrile.
As still another production process, a process of reacting fumaronitrile, maleonitrile or a chlorine-substituted compound thereof, or a mixture of these compounds with sulfur chloride in an aprotic polar solvent is known (see Patent Document 6). Fumaronitrile, maleonitrile and a chlorine-substituted compound thereof, or a mixture of these compounds, which is/are used in this process, can be produced from succinonitrile (see Examples 7 and 8 of Patent Document 6). However, it is desired that the production process described in Patent Document 6 is further improved in that this process requires two steps from succinonitrile.
In addition, it is considered that fumaronitrile, maleonitrile or a chlorine-substituted compound thereof has an industrially significant sublimation property. Compounds having a sublimation property generally have the potential of causing clogging of a reflux condenser or a pipeline in a plant by sublimation thereof. For this reason, the process described in Patent Document 6 has the drawback of having the possibility of requiring attention and measures in operations in its industrial implementation.
Besides, this process essentially requires an aprotic polar solvent such as N,N-dimethylformamide. And the recycle of the aprotic polar solvent is accompanied by difficulty because of working-up using water. Therefore, there is a drawback that it is highly possible that the used aprotic polar solvent becomes a part of waste. In addition, in this process, there is an example in which N,N-dimethylformamide and sulfur chloride, which is a chlorine compound, are used simultaneously. Therefore, there is a possibility that this process requires attention and measures with the view of preparing for any situation. Therefore, there is still room for improvement in this process.
Meanwhile, as a production process of 3,4-dichloro-5-cyanoisothiazole, a process using succinonitrile, sulfur and chlorine is known (see Patent Document 7). However, this process also requires N,N-dimethylformamide as a solvent. That is, since N,N-dimethylformamide and chlorine are used simultaneously, there is a possibility of the runaway of the reaction and an explosion. For this reason, it is considered that the implementation of this process also requires most careful attention and adequate measures in order to maintain safety. In addition, there is a possibility that this process cannot ensure the safety of a production plant because there is a possibility that the runaway of the reaction and an explosion occur in some cases as described above. That is, this process using N,N-dimethylformamide and chlorine at the same time is not preferred for industrial manufacture because there is concern for lack of safety.
Besides, the process described in Patent Document 7 essentially requires an aprotic polar solvent such as N,N-dimethylformamide. And the recycle of the aprotic polar solvent is accompanied by difficulty because of working-up using water. Therefore, there is a drawback that it is highly possible that the used aprotic polar solvent becomes a part of waste. That is to say, there is still room for improvement in this process.    Patent Document 1: U.S. Pat. No. 3,341,547 A    Patent Document 2: DE 2231097 A (DT 2231097)    Patent Document 3: DE 2231098 A (DT 2231098)    Patent Document 4: Japanese Patent Application Laid-Open No. Hei-5-59024 (JP-A-1993-59024)    Patent Document 5: Japanese Patent No. 4088036    Patent Document 6: International Publication No. WO2010/126170    Patent Document 7: Japanese Patent Application Laid-Open No. 2010-260805 (JP 2010-260805 A)